As a variable displacement compressor provided in a refrigeration circuit of an air conditioning system for vehicles, etc., a compressor such as one disclosed in JP-A-11-107929 is known. To this variable displacement compressor, in order to control its displacement for discharge, a displacement control valve is provided, in which a control point for a pressure in a suction chamber is decided to be one-to-one relative to an amount of electricity applied to an electromagnetic actuator, and which can maintain the variable displacement compressor forcibly at a minimum displacement condition when it is not excited.
This displacement control valve is structured as depicted in FIG. 4, and it comprises a valve casing 111, a bellows 112 as a pressure sensing member for sensing a pressure in a suction chamber or a crank chamber which is disposed in valve casing 111 and in which a spring 112a is disposed at a vacuum condition therein, a guide 113 receiving the lower end of bellows 112 and supported movably by valve casing 111, a spring 114 urging guide 113 upward, an adjustment screw 115 forming a part of valve casing 111 for adjusting an amount of expansion/contraction of bellows 112, a transmission rod 116 being brought into contact with the upper end of bellows 112 and supported movably by valve casing 111, a valve element 118 being brought into contact with the other end of transmission rod 116 and opening and closing a communication passage 117 between a discharge chamber and the crank chamber of the variable displacement compressor in response to the expansion/contraction of bellows 112, and an electromagnetic coil 121 generating an electromagnetic force for urging valve element 118 in its valve opening direction via a plunger 119 slid in a housing 110 and a transmission rod 120 slid in a fixed iron core 121a. 
Further, a surface 118b of valve element 118 opposite to a contact surface 118a being brought into contact with the valve seat is formed so as to receive a pressure in a crank chamber through a pressure guiding passage 122. A pressure receiving area for a pressure in a crank chamber of contact surface 118a side of valve element 118 and a pressure receiving area for a pressure in a crank chamber of surface 118b opposite thereto are set at almost the same area. Further, a side surface 118c of valve element 118 is supported movably by valve casing 111, a gap between the side surface 118c and the inner circumferential surface of valve casing 111 is set very small, and in this portion, valve element 118 is substantially slid in its axial direction.
In the above-described mechanism of the displacement control valve of the variable displacement compressor, although a pressure in a crank chamber is controlled by moving and controlling valve element in its axial direction, thereby controlling the displacement for discharge, totally four sliding parts between transmission rod 116 and valve casing 111, between side surface 118c of valve element 118 and valve casing 111, between transmission rod 120 and fixed iron core 121a and between plunger 119 and housing 110 are present in this mechanism for movement and control in the axial direction of valve element 118. Therefore, when valve element 118 is moved and controlled in its axial direction, because there occur sliding resistances in the respective sliding parts, if these sliding resistances are great, there is a fear to deteriorate the movement of valve element 118. Moreover, because four sliding parts are arranged in the same axial direction, it may be difficult to maintain the respective sliding parts accurately at respective predetermined positional relationships without shifting, and also from this point of view, there is a fear to enlarge the sliding resistance. If the movement of valve element 118 is deteriorated by such a sliding resistance, a smooth control of displacement for discharge of the variable displacement compressor may be damaged.